Utilization of gas burners in the above-mentioned field is known, for heating and drying purposes. With respect to preparation of the gas-air mixtures, the existing burners can be divided in two categories: premixed and nozzle-mixed types. The premixed technique (see for instance a catalogue of “Buzzer”, Charles A. Hones Inc. P.O. Box 510. 607 Albany Ave. NO. Amityville, N.Y. 11701, USA) provides for a high quality combustion, however it requires the use of special devices for flashback flame prevention. Additionally, the technique cannot be used in furnaces using mixtures with high excess of air, or in pressurized furnaces, or in furnaces operating over a wide range of the gas flow.
The nozzle-mixed burners (see for instance an “Eclipse Tempered Air Burners”, Rockford, Ill. 61103 (8155) 877-301; U.S. Pat. No. 3,044,537; Canadian Patent 661,577) do not suffer from flash-back flame effects, and are therefore exempt from utilizing non-return valves or other means to prevent flash-back fires. In such burners a combustible gas is made by mixing a hydrocarbon gas with air and igniting the mixture at the exit of the nozzle as soon as practical. The employment of such a technique, allows for an intentional flame temperature reduction by use of either an “on-ratio” mixture (about a stoichiometric gas:air ratio) or an excess of air. However, for this type of operation special care should taken to adapt the burners to the use of different sources of hydrocarbon gases, in order specifically to stabilize the flame and prevent soot formation in case of incomplete combustion. Some modifications of both types of burning techniques are current in the industry. Known in the art are combinations of a plurality of hydrocarbon gas and air nozzles, aimed at restricting the burning area. However, each modification is restrictive with respect to the terms of use, to avoid uncalled for effects.